batchFeaturizer vs adhoc

[vivace]

Hi

I am writing some code where it is convenient to do :

ListOfIds.take(100000).map(id => getExamples(id)).map(indexer).toIndexedSeq

I feel like this is not necessarily very efficient.... should I always use batchFeaturizer for this type of thing? Has it been optimized for memory efficiency whereas the above is not? 

cheers